But Taj Hargey, the imam at Oxford Islamic Congregation, said while Johnson’s choice of language was unfortunate, the burka and niqab are “a nefarious component of a trendy gateway theology for religious extremism and militant Islam”.

Writing in The Times, he said facial maskings were “un-Muslim” and contributed to “gender-inequality and inhibiting community cohesion”.

Johnson has yet to comment on the row triggered by his Daily Telegraph column on Monday - but has show no sign of backing down.

Critics have accused Johnson of using the row to win right-wing support in any future leadership battle.

Former attorney general Dominic Grieve said he would quit the party if Johnson became leader, while ex-minister Anna Soubry said that “many” One Nation Tories would also leave.

Lord Sheikh, the president of the Conservative Muslim Forum, said “severe action” should be taken against Johnson, including the withdrawal of the party whip.

But other Tories have come to Johnson’s defence. Jacob Rees-Mogg, the leading backbench Brexiteer, said May was “clearly wrong” to have demanded Johnson apologise.

Andrew Bridgen, the Tory MP for North West Leicestershire, said he felt “uncomfortable” speaking to a woman in a burka as you can’t see their reaction and it goes against “millions of years of human evolution”.

In his column, Johnson said Denmark was wrong to ban the burka, even if it was “oppressive”.

“It is absolutely ridiculous that people should choose to go around looking like letter boxes,” he wrote.

Johnson added: “If a constituent came to my MP’s surgery with her face obscured, I should feel fully entitled – like Jack Straw – to ask her to remove it so that I could talk to her properly.

“If a female student turned up at school or at a university lecture looking like a bank robber then ditto.”